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Climate Change: Theory and Forecasts

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Title: Climate Change: Theory and Forecasts


1
Climate Change Theory and Forecasts
  • David Gay
  • National Atmospheric Deposition Program (NADP)
  • dgay_at_uiuc.edu, (217) 244-0462

2
  • Two Parts
  • What exactly is climate change?
  • Theory
  • What we know
  • Forecasts

3
So, what is Climate Change?
4
First, what is climate?
  • Definition
  • Average course or conditions of weather at a
    place, usually over a period of years, as
    exhibited by
  • Temperature
  • Wind velocity
  • Precipitation (Websters)
  • Prevailing set of weather conditions
    (temperature, humidity, etc.)

5
So, can WE change climate?
  • Thomas Jefferson guessed we could in early 1800s
  • Trees in VA
  • Started making measurements
  • Urban concrete, no trees
  • Chemical composition of the atmosphere
  • Sensible energy vs. latent heating
  • Albedo changes
  • Natural changes (ice ages, warm periods)
  • Changing evaporation/precipitation (trends)
  • Other patterns (Malenkovitch cycles, el Nino/la
    Nina)
  • Cloud cover changes?

6
Definition of Climate Change
  • IPCC usage
  • Any change in climate over time, whether due to
    natural variability or from human activity.
  • Alternate
  • Change of climate, attributed directly or
    indirectly to human activity, that
  • Alters composition of global atmosphere and
  • Is in addition to natural climate variability
    observed over comparable time periods

7
So?
  • More than just temperature
  • Precipitation (amount and patterns)
  • Atmospheric pressure
  • Humidity
  • Circulation changes
  • Number of storms, droughts, freezes, etc.
  • And more.

8
Average Temperatures, in ?C
9
Type of Ecosystem, w T and P
10
Water Cycle
11
Radiation BalanceThe Greenhouse
  • Example
  • Your stove top

12
Radiation Balance
13
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14
Effective Greenhouse Gases
Atmospheric Window
15
So, what do we know? INTERGOVERNMENTAL PANEL
ON CLIMATE CHANGE (World Meteorological
Organization UN Env. Program) http//www.ipcc.ch
/
16
Carbon Dioxide Concentration Over Time
17
Methanealso a Greenhouse Gas
18
Quiz
  • How much has the earth warmed in the last 150
    years?

19
Answer
  • 0.95C (1.62 F) since 1850

20
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21
Historic Thermometer Records
22
Diurnal Temperature Range
23
Temperature Trends, ?C
24
Changes In..
25
Sea-Level Rise
Total Change 170 mm or 6.7 inches
26
Causes of Sea Level Rise
Sea-level rise during the 20th century (cm) Sea-level rise during the 20th century (cm)
Ocean thermal expansion 4
Mountain glaciers 5
Greenland Antarctic ice 2
Total 11
Observed rise 17
27
Arctic Sea Ice
2007 4.3 x106 km2 , record low
28
Glacial Retreat
Argentiere Glacier, French Alps
29
Trends in Precipitation
30
IPCC Summary of Observations
  • Global mean surface temperatures have risen
  • By 0.74C 0.18C over the last 100 years
    (19062005)
  • 2005 was one of two warmest years on record
  • Land regions have warmed at a faster rate than
    the oceans.
  • Changes in extremes of temperature are consistent
    with warming of climate
  • Widespread reduction in number of frost days in
    mid-latitude regions,
  • Increasing number of warm extremes reducing
    number of daily cold extremes observed in 70 to
    75 of land regions, and
  • Most marked changes are for cold (lowest 10,
    based on 19611990) nights, rarer over 1951 to
    2003 period.

31
IPCC Summary (cont.)
  • Sea-surface temperatures warming at all latitudes
    over all oceans,
  • Urban-heat island effects real but local, have
    not biased large-scale trends,
  • Average arctic temperatures increased at almost
    twice global average in past 100 years,
  • Lower-tropospheric temperatures increases
    slightly greater than those at surface between
    1958 to 2005

32
IPCC Summary (cont.)
  • Lower stratospheric temperatures cooling since
    1979,
  • Precipitation has generally increased over land
    north of 30N between 1900 to 2005, but downward
    trends dominate tropics since 1970s,
  • Droughts more common, especially in tropics and
    subtropics, since 1970s,
  • Changes in large-scale atmospheric circulation
    apparent

33
Historical Perspective of Temperatures
34
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35
Human Contribution to Climate Change (in one
slide) IPCC, 2007
36
Causes of climate change
Changes in atmospheric composition (greenhouse)
Volcanic eruptions
  • Climate change is driven by five causes
    (forcings)
  • Internal components of the climate system respond
    by changing and interacting in many ways

37
Natural Causes of Climate Change( non
anthropogenic)
38
Milanchovitch Cycles, Orbital Changes
today
  • Earth orbital changes
  • Result from cyclic variations in Earth's orbit
    around the Sun
  • Alter the amount of solar radiation (insolation)
    received on Earth by season and by latitude

39
Precession of the equinoxes (23k
years) Oval/circular changes Inclination Change
40
Changes in Solar Energy Output
41
  • The smoothed sunspot curve correlate with
    temperature
  • Some intervals almost entirely lack sunspots,
    such as the Maunder sunspot minimum from
    1645-1715 AD
  • These sunspot minima occurred during the Little
    Ice Age when the sun was 0.25 weaker
  • Solar activity was generally high during the
    Medieval Warm Period

42
Other Natural Causes
Mt Pinotubo
43
The Modeled Future
44
CO2 Should Increase
45
Predicting TemperatureGlobal Climate Models
(GCMs)
  • Physical equations
  • Lots of computing
  • Divide the globe
  • into little boxes

46
Forecast Temperatures
47
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48
Projections of Surface Temperatures
49
How Good Are the Models?
50
Further Reading
  • Intergovernmental Panel on Climate Change (IPCC)
  • UN organization (Weather Meteorological Office)
  • http//www.ipcc.ch/
  • Summary for the physical science basis
  • http//ipcc-wg1.ucar.edu/wg1/wg1-report.html

51
Figures from W. Ruddiman, 2008 Earths Climate
Past and Future
52
Climate Change Theory and Forecasts
  • David Gay
  • National Atmospheric Deposition Program (NADP)
  • dgay_at_uiuc.edu, (217) 244-0462
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